How to Replace an Audi G28 Engine Speed Sensor
In this video, Charles the Humble Mechanic shows how to replace the G28 engine speed sensor. This sensor is situated at the edge of transmission over the flywheel gear. It transmits a signal to the ECU via a grey wire T55/49, then to the tachometer on the instrument cluster.
1. Engine Speed Sensor
It is located on the outside of the transmission, above the flywheel ring gear G28 Engine Speed Sensor sends an electrical signal to ECU pin T55/49 using an uncolored wire. The ECU then uses this information to control the boost, fuel, and timig. It also sends an alert to the G5 Tachometer located in the instrument cluster.
The sensor is used to correlate the G40 Camshaft position Sensor. The ecu must be aware when the crankshaft is TDC and where the camshaft is located so that it can start spark and injectors according to the situation.
If this sensor fails when it fails, the ECU will display an error code P00160. This means that the Crank Shaft is out of alignment with the Intake Camshaft. It could also be a sign of an issue with the chain or a jump in the chain link of the upper timing chain. However talking to will not be displayed on its own without additional information from other sensors (G4 and G40).
It's a bit tricky to test since there are various pins on the connector, and each has its own functions. The best method for doing this is to measure the resistance between the ECU and the sensor. It should read about 1000 ohms when it is operating at its maximum. If you're having issues with this sensor, look for signs of oil or coolant in the connector bay.
2. Injectors
Yesterday, as i was accelerating off the highway paytoll at a high speed I noticed a significant decrease in power. It was as if the engine had run out of gas. Or, my injectors were not firing. I pulled out the spark plugs this morning, three were soaked with gasoline and the fourth was unclean. When i crank the engine, there are no sparks i put tissue on the top of each hole in the injector and the 3 drenched with gazoline jump out but the 4th stays closed. I checked the ground connection of ECU pins 14,30 and 48/55. I found 0ohm. I think the issue is somewhere else.
I also tried to reset the PID but without success. The car is able to start if the G28 is unplugged and runs fine when it is connected, but still is experiencing intermittent misfires at higher RPM. The coolant sensor (G62), even when unplugged, still shows temperatures of -49c. I also noticed that the oil pressure gauge in the cockpit shows 2 bar while the actual pressure is 0.0 when i rev the engine.
I don't know what to do. I believe that I've all other possibilities out. However, i'm afraid that i might have missed something. Let me know if you have any ideas! TIA!
3. Fuel Pump
The fuel pump in the g28 receives signals from the RPM sensor. The GM-style transmitter is identical to the G4 and both function in the 80 100 200, UrS and RS2 cars which is why you can easily locate one at a junkyard or in a local parts store. Test them out to do - just put your DMM in resistance mode and take measurements between pins 1 (with the bump on the connector end up) and 2 (2nd from left on the black connector's end). They must be infinite Ohms.
4. ECU
The ECU of our 20vt turbo (3B AAN ABY) engines requires to know the position and speed the crankshaft to determine timing of the fuel injector, etc. It uses a Crank Position Sensor G4 and an Engine Speed Sensor G28 to achieve this. If either of these sensors go wrong, you will receive codes on the diagnostic scanner which could cause engine shut down.
The signs of a failing G28 sensor include an inaccurate gearbox rev counter, gears shifting quicker than normal and/or a misfire when you are in gear. It is possible that your sensor is failing and needs to be replaced if you notice any of these symptoms. The good news is they are very cheap and easy to find particularly when you're looking at an Bosch sensor, which is what ours are. Alternatively, the GM version of this unit is also a good choice.
5. Tachometer
A malfunctioning engine speed sensor could be the cause of a slew of issues with your car. It's an essential component of the transmission of your Audi because it relays information to the ECU about how fast or slowly the engine of the car is turning. When this sensor fails, it could cause problems for the transmission as well as the other car's components.
The G5 engine speed sensor is located on the outside of the transmission just above the flywheel ring gear. It transmits a signal to the ECU at pin T55/49 through a grey wire. The ECU then uses and processes this signal to regulate fuel, timig and boost, and also sends it on to the G5 tachometer in the instrument cluster. You can test for sensor failure by checking continuity from the sensor to the tachometer. Also, you can check continuity between pin T55/49 of the ECU and pin T6a/1 of the instrument cluster (trace [79trace [79]) and between pin T6a/1 and pin T26a/12. You should see around 1000 ohms of resistance between these two points. This is a typical part across the Audi 80, 100 200, UrS and RS2 range from 1985 MC to the 1997 UrS AAN and 1995 RS2 ADU, so the best parts could be found in wrecking yards.